Introduction to Matlab

Introduction to Matlab By: İ.Yücel Özbek

Outline: • Matlab Screen • Variables, array, matrix, indexing • Operators (Arithmetic, relational, logical ) • Display Facilities • Flow Control • Using of M-File • Writing User Defined Functions • Conclusion

Matlab Screen • Command Window • type commands • Current Directory • View folders and m-files • Workspace • View program variables • Double click on a variable to see it in the Array Editor • Command History • view past commands • save a whole session using diary

int a; double b; float c; Variables • No need for types. i.e., • All variables are created with double precision unless specified and they are matrices. • After these statements, the variables are 1x1 matrices with double precision Example: >>x=5; >>x1=2;

Array, Matrix • a vectorx = [1 2 5 1] x = 1 2 5 1 • a matrixx = [1 2 3; 5 1 4;3 2 -1] x = 1 2 3 5 1 4 3 2 -1 • transposey = x’ y = 1 2 5 1

Long Array, Matrix • t =1:10 t = 1 2 3 4 5 6 7 8 9 10 • k =2:-0.5:-1 k = 2 1.5 1 0.5 0 -0.5 -1 • B = [1:4; 5:8] x = 1 2 3 4 5 6 7 8

zeros(M,N) MxN matrix of zeros ones(M,N) MxN matrix of ones rand(M,N) MxN matrix of uniformly distributed random numbers on (0,1) x = zeros(1,3) x = 0 0 0 x = ones(1,3) x = 111 x = rand(1,3) x = 0.9501 0.2311 0.6068 Generating Vectors from functions

Matrix Index • The matrix indices begin from 1 (not 0 (as in C)) • The matrix indices must be positive integer Given: A(-2), A(0) Error: ??? Subscript indices must either be real positive integers or logicals. A(4,2) Error: ??? Index exceeds matrix dimensions.

Concatenation of Matrices • x = [1 2], y = [4 5], z=[ 0 0] A = [ x y] 1 2 4 5 B = [x ; y] 1 2 4 5 C = [x y ;z] Error: ??? Error using ==> vertcat CAT arguments dimensions are not consistent.

Operators (arithmetic) + addition - subtraction * multiplication / division ^ power ‘ complex conjugate transpose

Matrices Operations Given A and B: Addition Subtraction Product Transpose

Operators (Element by Element) .* element-by-element multiplication ./ element-by-element division .^ element-by-element power

The use of “.” – “Element” Operation A = [1 2 3; 5 1 4;3 2 1] A = 1 2 3 5 1 4 3 2 -1 b = x .* y b= 3 8 -3 c = x . / y c= 0.33 0.5 -3 d = x .^2 d= 1 4 9 x = A(1,:) x= 1 2 3 y = A(3 ,:) y= 3 4 -1 K= x^2 Erorr: ??? Error using ==> mpower Matrix must be square. B=x*y Erorr: ??? Error using ==> mtimes Inner matrix dimensions must agree.

Basic Task: Plot the function sin(x) between 0≤x≤4π • Create an x-array of 100 samples between 0 and 4π. • Calculate sin(.) of the x-array • Plot the y-array >>x=linspace(0,4*pi,100); >>y=sin(x); >>plot(y)

Plot the function e-x/3sin(x) between 0≤x≤4π • Create an x-array of 100 samples between 0 and 4π. • Calculate sin(.) of the x-array • Calculate e-x/3 of the x-array • Multiply the arrays y and y1 >>x=linspace(0,4*pi,100); >>y=sin(x); >>y1=exp(-x/3); >>y2=y*y1;

Plot the function e-x/3sin(x) between 0≤x≤4π • Multiply the arrays y and y1 correctly • Plot the y2-array >>y2=y.*y1; >>plot(y2)

Display Facilities • plot(.) • stem(.) Example: >>x=linspace(0,4*pi,100); >>y=sin(x); >>plot(y) >>plot(x,y) Example: >>stem(y) >>stem(x,y)

Display Facilities • title(.) • xlabel(.) • ylabel(.) >>title(‘This is the sinus function’) >>xlabel(‘x (secs)’) >>ylabel(‘sin(x)’)

Operators (relational, logical) • == Equal to • ~= Not equal to • < Strictly smaller • > Strictly greater • <= Smaller than or equal to • >= Greater than equal to • & And operator • | Or operator

Flow Control • if • for • while • break • ….

Some Dummy Examples if ((a>3) & (b==5)) Some Matlab Commands; end if (a<3) Some Matlab Commands; elseif (b~=5) Some Matlab Commands; end if (a<3) Some Matlab Commands; else Some Matlab Commands; end Control Structures • If Statement Syntax if (Condition_1) Matlab Commands elseif (Condition_2) Matlab Commands elseif (Condition_3) Matlab Commands else Matlab Commands end

Some Dummy Examples for i=1:100 Some Matlab Commands; end for j=1:3:200 Some Matlab Commands; end for m=13:-0.2:-21 Some Matlab Commands; end for k=[0.1 0.3 -13 12 7 -9.3] Some Matlab Commands; end Control Structures • For loop syntax for i=Index_Array Matlab Commands end

Control Structures • While Loop Syntax while (condition) Matlab Commands end Dummy Example while ((a>3) & (b==5)) Some Matlab Commands; end

Use of M-File Click to create a new M-File • Extension “.m” • A text file containing script or function or program to run

Use of M-File Save file as Denem430.m If you include “;” at the end of each statement, result will not be shown immediately

Writing User Defined Functions • Functions are m-files which can be executed by specifying some inputs and supply some desired outputs. • The code telling the Matlab that an m-file is actually a function is • You should write this command at the beginning of the m-file and you should save the m-file with a file name same as the function name function out1=functionname(in1) function out1=functionname(in1,in2,in3) function [out1,out2]=functionname(in1,in2)

Same Name Writing User Defined Functions • Examples • Write a function : out=squarer (A, ind) • Which takes the square of the input matrix if the input indicator is equal to 1 • And takes the element by element square of the input matrix if the input indicator is equal to 2

Writing User Defined Functions • Another function which takes an input array and returns the sum and product of its elements as outputs • The function sumprod(.) can be called from command window or an m-file as

Notes: • “%” is the neglect sign for Matlab (equaivalent of “//” in C). Anything after it on the same line is neglected by Matlab compiler. • Sometimes slowing down the execution is done deliberately for observation purposes. You can use the command “pause” for this purpose pause %wait until any key pause(3) %wait 3 seconds

Useful Commands • The two commands used most by Matlab users are >>help functionname >>lookfor keyword

Questions • ? • ? • ? • ? • ?

Thank You…

Introduction to Matlab